The mechanism of action of a variety of drugs on neuromuscular transmission will be studied by means of microelectrode and voltage clamp techniques. Special emphasis is placed on the dual action of certain depolarizing blocking agents, one being the direct end-plate blocking action at relatively low concentrations and the other being the indirect blocking action due to end-plate depolarization at higher concentrations. Nicotine and fire ant venoms have been found to possess such dual action in our previous study. Other so-called depolarizing and non-depolarizing blocking agents will be examined for their possible dual mechanism of action. The drugs to be studied include succinylcholine, decamethonium, gallamine, pancuronium, etc. This study is expected to give the basis of the cellular mechanism of action of neuromuscular blocking agents.